Just tell them the truth, that this isn't what you wanted, but that you're fighting for your marriage and your family. Tell them you still love her, but that you have to protect yourself, and you felt they should know the truth.
Do not talk to OM -- it serves no purpose, and elevates him in importance. If he's married, however, you should expose the affair to his wife.
I'm so sorry, Twolf -- I know this sucks. My bomb day was three years ago almost to this day! Today we are reconciled, so I know that anything is possible.
